[Sursound] Coefficients for Octagonal Decoder with CF

[Richard Graham]

Hi list!

Can anyone point me to a set of coefficients for an octagonal decoder with CF 
similar to the coefficients on Blue Ripple Sound?

http://www.blueripplesound.com/decoding 


All the best,

Ricky
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Re: [Sursound] grambilib~ for Pd

[Richard Graham]

Hi Aaron,

Thank you for taking the time to look at the source; good catch! I’ll fix those 
issues immediately.

Ricky

> On Mar 11, 2016, at 12:00 PM, sursound-requ...@music.vt.edu wrote:
> 
> Hi Ricky,
> 
> I took a quick look at grambipan.c.  For FuMa U you've written
> 
> 189:   (*APout4++) = sample1 * (2 * cosf(sample2)) * cosf(sample3) *
> cosf(sample3); //U
> 
> whereas the correct expression (found on Richard Furse's webpage, for
> example) is
> 
> U:cos(2A) cos(E) cos(E)
> 
> Please note that cos(2x) does not equal 2cos(x).  I see similar problems in
> other definitions.
> 
> 
> You might want to take a look at my Python library,
> symbolic_spherical_harmonics.  It derives and writes out expressions for
> the spherical harmonics in a number of different languages.
> 
> $ python SymYlm.py --spherical --FuMa --four_pi --translation c 2 2
> pow(cos(phi), 2)*cos(2*theta)
> 
> $ python SymYlm.py --cartesian --FuMa --four_pi --translation c 2 2
> pow(x, 2) - pow(y, 2)
> 
> Here's the git repo:
>   https://bitbucket.org/ajheller/symbolic_spherical_harmonics 
> 
> 
> --
> Aaron (hel...@ai.sri.com )
> Menlo Park, CA  US

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[Sursound] grambilib~ for Pd

[Richard Graham]

Hi all,

I’ve been working on a simple ambisonics library for Pd. 

Here’s v1:

https://github.com/rickygraham/grambilib 


I would love to hear your thoughts!

Ricky
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Re: [Sursound] Ambisonic Decoder Design Resources

[Richard Graham]

Folks, many thanks for all these incredibly helpful resources.
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Re: [Sursound] Ambisonic Decoder Design Resources

[Richard Graham]

Hi Archontis,

I would like to design decoders for 2d and 3d arrays, 1st through 3rd order (at 
least), both regular and irregular arrays. C code examples would be incredibly 
helpful as I plan to develop decoders for Pd and Max.

I have already developed some basic ambisonic externals for Pd 
(http://rickygraham.net/?p=176401730 ) 
based on encoding and decoding technical notes from Blue Ripple Sound 
(http://www.blueripplesound.com/decoding 
), which provides coefficients for 
basic array set-ups. 

Most importantly, I’d like to figure out how to calculate these coefficients 
myself and I am having trouble finding literature on how to do that. I have 
reached out to a few folks who used their own programs to calculate 
coefficients. Essentially, I’d like to build my own program in the C 
programming language. 

Shortly, I will have access to a 16-channel ring on the horizontal plane and a 
b-format cube. This system will be modular and configurable into irregular 
setups, too. 

Many thanks,

Ricky

> On Feb 20, 2016, at 12:00 PM, sursound-requ...@music.vt.edu wrote:
> 
> Hi Richard,
> 
> there are numerous articles, do you intend to use anything more specific? 2D 
> or 3D decoding? regular or irregular setups? Or you are looking for the most 
> general case?
> (when you say in C, do you mean published code examples?)
> And by low-orders do you mean first-order systems mainly (b-format)? Most 
> practical systems at the moment target up to 3rd-order, which are not very 
> high orders either, but it makes a difference.
> 
> Regards,
> Archontis

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[Sursound] Ambisonic Decoder Design Resources

[Richard Graham]

Hi all,

Can anyone recommend literature on designing ambisonic decoders (in C)? 
Specifically, articles that speak to the calculation of coefficients for 
low-order decoders. 

All the best,

Ricky
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Re: [Sursound] ambilib~ in C

[Richard Graham]

Dave wrote: 

>  -KPi/2 to +KPi/2 for elevation since we generally
> regard horizontal as 0 degrees (or radians) with downward angles negative
> and upward angles as positive. 

Hi Dave,

Thanks, this does make sense. For anyone else interested:

Elevation for ambipan~ is defined as: x->APdELeft = (x->APfElevationLeft - 0.5) 
* kPI;
kPI = 3.14159265358979323846
x->APfElevationLeft = elevation input for, in this case, the left-most audio 
input
All input parameters are scaled 0 to 1. 
0 to 1 input offset by -0.5 gives us -0.5 to 0.5 range. 
Multiply that by 3.141 give us -KPi/2 to +KPi/2 (-1.5705 to + 1.5705)

Great! Thanks.

All the best,

Ricky

> 0 to 1 - 0.5)  * kPI.
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[Sursound] ambilib~ in C

[Richard Graham]

Hi all,

I have some quick questions; I’m writing my own audio-rate control version of 
the ambilib~ library for Pd / Max and I wanted to clarify the following:

The elevation param has an offset of -0.5: (x->APfElevationRight - 0.5)  * kPI. 

1) Why is that? 

2) The unit for elevation is radians, yes?

All the best,

Ricky


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